This invention relates in general to multi-address alerting devices employed in a system for alerting one or some of a large number of persons from a central paging station. In practice, for example, a caller of such a person may reach the central station by telephone, and the paging station may signal to the person via a radio common carrier (RCC) link. The invention thus relates more particularly, by way of example, to personal paging devices which can be carried on the person of a user, for response to space-transmitted calling signals such as radio waves. Alert signals provided by such devices may be audible, visible or tactual (e.g.: vibratory), and alerting devices are known which give the user a choice of one or more alerting modes. Whatever alerting mode or modes are employed in a particular alerting device, the user must be wearing the alerting device, or at least be sufficiently close to it to perceive the alerting signal, in order for the alerting device to accomplish its purpose. This invention is addressed generally to situations in which a user of an alerting device which is energized to receive calling signals nevertheless fails for one reason or another to perceive an alerting signal that is provided by the device in response to a calling signal; and more particularly to the effective use in such situations of an alert device that has the capability of issuing an alerting signal in one of two or more different modes in response to a calling signal which is addressed to one only of the available modes.
In the art of paging persons by means of portable alerting devices, such as radio receivers carried on the person that are responsive to an assigned carrier frequency, it is known to modulate the carrier with a sequence of calling frequencies, or "tones", for the purpose of signalling to subscribers with unique combinations of tones, for example, to address a particular subscriber, or to broadcast a particular message. A known two-tone paging system uses two tones selected in a coded sequence from an array of available tones. In another system, five tones are sent out (i.e.: modulate the carrier) in a coded sequence, but the number of tones used in a given coded sequence is not critical. In any system, each individual receiver is responsive, through a tone-responsive network or the like, to a selected one or few of all the possible useful codes. In a five tone paging system which is in common use, each tone last 33 milliseconds, and there is a 35 millisecond gap between pages, resulting in (5 .times. 33) + 35 = 200 milliseconds for a complete page. Such a 5-tone paging system allows five pages per second. Thus, an alerting device in such a system has one-fifth of a second to receive a calling or paging signal and to provide an alerting signal in response to it. The alerting signal can, however, have duration and form which are each independent of the duration and form, respectively, of the paging signal.
Paging systems are known which provide the user with two modes of alerting signal and means in the receiver automatically to select a particular mode in response to a particular tone-code modulation of the carrier. Such systems are sometimes known as "dual address" paging systems, and they add to the paging art the capability of addressing a choice of one of two possible messages to a particular subscriber.
Paging system receivers are known in which calling information is stored if not responded to within a specified time interval. An example is disclosed in the application for U.S. patent of James DeRosa, Ser. No. 532,059 filed Dec. 12, 1974, which is assigned to the same assignee as the present application. In alerting systems of the kind that is described by DeRosa, the receiver is provided with some means to terminate an alerting signal and to set the device in condition to respond to another paging or calling signal. In the described example, that means is a manually-operable switch labelled "reset"; and conveniently that switch is of the momentary-contact type. Upon perceiving an alert signal, the user operates the reset switch. If within a prescribed time interval after initiating an alert signal the alerting device does not receive from the user a signal (e.g.: operation of a reset switch) that the user has perceived the alert signal, the device itself automatically terminates the alert signal and stores in a page memory the information that a calling signal was received. This information is retained in the page-memory until the alerting device is de-energized (by being shut-off, or depletion of its power supply if a battery is used), or until the user operates the reset switch. Thereafter, if the reset switch is operated, the alerting device will again initiate an alert signal, and in that situation the reset switch functions additionally and alternatively as a recall switch. A second operation of this switch terminates the recalled alert signal and resets the receiver into condition for receiving another calling signal and providing an alert signal in response to it.